The natural history of HIV characteristically includes a myriad of hematologic manifestations. While experience has improved management of these complications, the impact of marrow dysfunction on the morbidity of these patients remains significant. Borderline marrow reserve in cytopenias complicate treatments for the retrovirus itself, opportunistic infections, and HIV related malignancies. As survival is prolonged for patients with AIDS, hematopoietic failure may present an even more prominent complication of end stage disease. More importantly, as gene therapy for HIV is pursued, understanding the etiology of marrow dysfunction in this disease is paramount. The objective of this proposal is to examine the roles of the hematopoietic microenvironment and the progenitor cell population in the pathogenesis of HIV-induced hematologic abnormalities. We hypothesize that HIV either directly or indirectly results in abnormal cytokine expression in the microenvironment to affect hematopoiesis. The specific aims are as follows: 1) To determine the effect of HIV infected stroma on hematopoietic cell proliferation and differentiation. Stromal cells, infected with HIV and analyzed by PCR in situ hybridization, will be studied in long term bone marrow culture. 2) To determine the effect of stromal cells from HIV positive patients on hematopoiesis. Stromal cells obtained from patients with early and late stage HIV will be cultured, their level of infection determined, and subsequent effects on hematopoietic cell proliferation evaluated. 3) To determine whether HlV infection alters stroma-derived cytokine production. HIV infected and patient derived stromal cells will be studied for their constitutive and stimulated cytokine production. Candidate cytokines including GMCSF, G-CSF, M-CSF, IL1, IL3, IL6, tumor necrosis factor, TGFbeta, stem cell factor, and basic fibroblast growth factor will be studied initially. 4) To analyze the hematopoietic progenitor cell population from patients with HIV. Specifically, CD34+ cells from patients with HIV will be studied: for HIV infection in single cells utilizing PCR in situ hybridization; for proliferative potential in long term bone marrow cultures in the presence of normal and patient stromal cells; and for mobilization and proliferative potential following G-CSF administration to patients with HIV. The results of these studies will be useful in designing and assessing. the feasibility of HIV directed therapy utilizing transplanted hematopoietic stem cells.